With the rapid spread of resistance of plant pathogen populations to synthetic fungicides and increased awareness of human to environmental pollution, an alternative means of control plant diseases is very necessary. The most effective means is to boost the plant defense mechanisms by induced plant resistance [L. C. van Loon, P. A. H. M. Bakker, and C. M. J. Pieterse, Systemic resistance induced by Rhizosphere bacteria, Annu. Rev. Phytopathol. 1998. 36:453-83] and/or systemic acquired resistance [W. E. Durrant and X. Dong, Systemic acquired resistance, Annu. Rev. Phytopathol., 2004, 42:185-209]. Therefore, reducing and/or delaying the formation of pathogen resistance and protecting environments.
Induced resistance is a state of enhanced defensive capacity developed by a plant when appropriately stimulated [Kuc, J., Development and future direction of induced systemic resistance in plants, Crop Protection, 2000, 19, 859-861]. Induced plant resistance can be triggered by chemicals, nonpathogens, avirulent forms of pathogens. When induced resistance is systemic, it is commonly referred as systemic required resistance [L. C. van Loon, P. A. H. M. Bakker, and C. M. J. Pieterse, Systemic resistance induced by Rhizosphere bacteria, Annu. Rev. Phytopathol. 1998. 36:453-83].
Anthraquinone derivatives such as rhein, emodin, aloe-emodin, parietin, physcion, emodin-glycoside, physcion-glycoside, chrysophanol and chrysophanol-glycoside as well belong to one family of chemicals which induce plant resistance to pathogens. Induced resistance of this class of chemicals was well studied by using MILSANA® biofungicide, the commercial name given to the extract of giant knotweed [B. Fofana, D. J. McNally, C. Labbe, R. Boulanger, N. Benhamou, A. Seguin, R. R. Belanger, MILSANA® biofungicide induced resistance in powdery mildew-infected cucumber plants correlates with the induction of chalcone synthase and chalcone isomerase, Physiol. Molec. Plant Pathol. 2002, 61, 121-132]. Physcion and emodin are the major bioactive anthraquinone derivatives in MILSANA® biofungicide that is verified in our laboratory by bioassay-guided fractionation. Glycoside derivatives of physcion and emodin are the minor for the activity. Numerous other studies in the agricultural field have shown that many anthraquinone derivatives displayed strong bioactivities such as antifungal, antifeedant, antimicrobial, molluscicidal activity [S. K. Agarwal, S. S. Singh, S. Verma, S. Kumar, Antifungal activity of anthraquinone derivatives from Rheum emodi, J. Ethnopharmacol. 72 (2000) 43-46S; J. D. D. Tamokoua, M. F. Tala, H. K. Wabo, J. R. Kuiatea, P. Tane, Antimicrobial activities of methanol extract and compounds from stem bark of Vismia rubescens, J. Ethnopharmacol, 2009, in press; G. N. Krishnakumari, B. Bhuvaneswari, I. R. Swapna, Antifeedant activity of quinones from Ventilago madaraspatana, Fitoterapia, 72 (2001) 671-675; Y. Liu, F. Sporer, M. Wink, J. Jourdane, R. Henning, Y. L. Li and A. Ruppel, Anthraquinones in Rheum palmatum and Rumex dentatus (Polygonaceae), and phorbol esters in Jatropha curcas (Euphorbiaceae) with molluscicidal activity against the schistosome vector snails Oncomelania, Biomphalaria and Bulinus, Tropical Medicine and International Health, 1997, 2(2), 179-188]. Synergism also exists in the interaction of these compounds such as in the interaction between physcion and chrysophanol [X-J., Yang, L-J., Yang, S-N., Wang, D-Z., Yu, H-W., Ni, Synergistic interaction of physcion and chrysophanol on plant powdery mildew, Pest Manag Sci 63:511-515 (2007)].
To protect the environments, MILSANA® biofungicide, a product derived from Reynoutria sachalinensis, was formulated as a water-based Suspension Concentrate (SC), registered as a biochemical pesticide (U.S. Pat. No. 4,863,734 Process for combating fungi; U.S. Pat. No. 5,989,429, Processes for forming stabilized biochemical agricultural products). MILSANA® biofungicide is a very effective product for the control of mildew. However, two of the major problems that prevent it as a good commercial pesticide product are industrial reproducibility and the instability of the formulation. Reproducibility of making such a formulation is poor in industry. Because many chemicals in the extracts such as chlorophylls and anthraquinone derivatives are hydropbobic compounds, these compounds can aggregate together to form bigger particles as time passes by. Multiple difficulties are associated with such large particles. They are difficult to dissolve in water. Additionally, effective concentration of active ingredients in the application solution is decreased, resulting in worse efficacy; the big particles also can stick to the spraying containers and it is difficult to wash away with water. The big particles can even block the nozzles.